Apparatus for amplifying electrical



Dec. 19, 1939. J. E. PARKER APPARATUS FOR AMPLIFYING ELECTRICAL CURRENTS Original Filed Mai-ch 12, 1924 P mm P 8, 0000' 6;

gmanto'c James Parker Reissued Dec. 19, 1939 UNITED STATES PATENT OFFICE APPARATUS FOR AMTLIFYING ELECTRICAL CURRENT'S James E. Parker, Washington, D. 0.

Original No. 1,672,037, dated June 5, 1928, Serial No. 698,680, March 12, 1924. Application for reissue May 28, 1930, Serial No. 456,741

20 Claims.

While my invention relates generally to the amplification of electrical currents it has for a particular object the amplification of high frequency electrical currents modulated at low or 5 audible frequency. Modulations at audible frequency are variations of the envelope of the high frequency currents, said variations having a frequency within the audible range, While modulations at low frequency are variations of the envelope of the high frequency currents having any frequency below the audible range.

Heretoforewhen the same amplifying devices have been used for the dual function of amplifying high frequency currents and low or audible frequency currents, as for example in the well known reflex circuits, a difference of potential at high frequency existed between the points where the low or audible frequency currents were returned to the high frequency circuit.

This

enabled a high frequency potential to work back through the return path of the low frequency currents into the rectifier.

or audible Since the impedance of this return path was always substantially different from that of the intended path for the high frequency currents,

there were present in the rectifier two high frequency potentials of the same frequency but differing in phase. This cut of phase relation resulted in a substantial modification of the envelope of the high frequency currents present in the rectifier so that the output of the rectifier faithful reproduction of the envelope was not a of the high currents, using the same amplifying the dual function.

devices for My invention will be best understood by reference to the accompanying drawing in which it is illustrated in the figure employed as an amplifier in a receiving system for radio.

L1 represents a coil or loop receiver having a capacity tuning arrangement illustrated by C1. As the capacity C1 I preferably employ an air condenser having two sets of fixed one set of movable plates.

plates and The movable plates are controlled by one shaft and since these plates are of a low potential at all times, I have grounded them as shown in order to eliminate any stray capacity effects in the manipulation of the tuning of the resonant circuit.

Two three electrode vacuum tubes VT1 and VT2 have their grids g1 and 92 connected to opposite sides of the capacity C1. The grounded filament lead to these tubes is connected to approximately the mid point of the coil L1 through the secondary S1 of a low or audible frequency transformer A'I1. This lead also includes a biasing battery B2 to apply a negative potential to the grids of the vacuum tubes of a chosen value to obtain efiicient amplification. The plate circuits of tubes VT1 and VT2 are supplied with a source of energy B1 which causes currents to flow through choke coil I1 and telephone receiver I2, resistances R1 and R2, tuned circuit consisting of inductances L2 and L3 with condensers C2 and C3, and through plates P1 and P2 back to filaments F1 and F2 to battery B1. Inductively coupled to tuned circuit L2, L1, C2 and C3 is another tuned circuit containing inductances L4 and condenser C4. One side of this tuned circuit is connected to filament Fa of a vacuum tube'VTa and the other side to the grid 93. The vacuum tube. VTg is connected for rectification, having stopping condenser SC and grid leak 91 and not including a biasing potential on the grid. The plate P3 of this tube is connected to the source of energy B1 through the primary P of low or audio frequency transformer AT1, and the circuit is completed through the filament F3. The plate circuit connection to the battery B1 is shown as variable as the detector or rectifying tube does not require as much plate potential as do the amplifying tubes VT1 and VT2. The filaments of the tubes are supplied with heating current from the battery A1 in the usual manner. The condensers C2 and C3 are preferably constructed as described in connection with capacity C1. The choke coil I1 is not essential but I find it preferable to permit a larger current flow in the plate circuit of the vacuum tubes VT1 and VT2 than is ordinarily 0-btainable through the impedance of telephones or loud speaking devices I2. It is not essential to employ a tuned coupling between the plate circuits of vacuum tubes VT1 and VT2 and the grid circuit of the vacuum tube VT3 the tuned coupling I have shown being replaceable by an ordinary radio frequency transformer or other suitable transfer device, but such devices are not as selective as the tuned coupling I have shown. The resistances R1 and R2 are for the purpose of restricting the tendency of the vacuum tubes to create oscillations in tuned circuits, and these resistances should be chosen of such value as to just overcome this tendency so as not to destroy the amplitude of the amplified currents.

the amplifier tubes VT1 and VTz alternately with equal and'opposite potentials. By means of the biasing battery B2 the grids are worked at the most eificient potential for amplification according to my invention. The highly amplified currents are joined in the common plate circuit through the connection between the inductances L2 and Is. This amplified current is in its high frequency form and is transferred to the detector tube VTs by inductive coupling between coils L2 and In and resonant circuits LiCi. In the vacuum tube V'I's the amplified currents are converted into low or audible frequency currents through the rectifying action of the tube and its connections, these low or audible frequency currents being characteristic of the modulations in the high frequency currents. The low or audible frequency currents flowing through the plate circuit of the detector tube VT3 also flow through the'primary of the low or audio frequency transformer AT1 and induce current in the secondary S1 of this transformer.

As has been previously pointed out the grounded filament lead to the tubes VTi and VTz is connected to approximately the midpoint of the coil L1. This point of connection is a nodal point. There therefore exists no high frequency potential between the point of connection with the coil L1 and the grounded filament lead. In other words no high frequency potential exists across the transformer AT1. It follows that no high frequency potential can work back through the leads fromthe primary P of the transformer ATl to the rectifier tube VTs. Thus the high frequency potential present in the rectifier tube VT3 is only that which has reached the tube VTs through the intended path including the tubes VT1, VT2 and the resonant circuit L404. When a high frequency potential exists across the transformer AT1, or its equivalent in the usual reflex circuit, a substantial high frequency potential will work back into the rectifier tube because the impedance of this alternate path, although designed for other than high frequency, is, nevertheless, due to distributed capacity or other causes sufficiently low, to allow the passage of enough high frequency potential to effect the rectifier undesirably. It should furthermore be noted that it requires but a slight high frequency potential out of phase with the desired high frequency potential to substantially modify the envelope of the high frequency potential present in the detector.

With the present invention the output of the detector tube VTs is a faithful reproduction of the envelope of the high frequency currents as received by the system. The mathematical analysis will show that with suitable transformer connections the potential induced in the transformer ATi by the low or audio frequency currents, neglecting certain higher harmonics, is in phase with the change of the internal resistance of the tube VT: which in turn is in phase with the envelope of the incoming high frequency currents.

There is thus present in the transformer AT1 a low or audible frequency voltage in phase with the envelope of the incoming high frequency signals. This low or audihie frequency voltage is applied to the grids g1 and oz of the tubes VT1 and. Tz causing he average potential of the grids g1 and oz to rise and fall together and in phase with the envelope of the incoming high frequency currents.

With the grids of tubes VT1 and VTz normally biased by means of battery B2 to the potential most efficient for amplification, it is apparent that any low or audio frequency potential supplied by means of the transformer AT1 is either added to or subtracted from the potential normally applied to the grids g1 and g2 thus causing the potential of these grids to depart from the potential most efficient for amplification. The result of this action is to decrease the strength of the high frequency output of tubes W1 and VTz responsive to a strong signal while permitting the amplifier to work at maximum efficiency when very weak signals are being received.

It is further obvious that the voltage returned to the high frequency circuit through the transformer AT1 may be either of low frequency or of audible frequency according to the chosen impedance characteristic of the transformer AT1, and that, if the high frequency currents are modulated at a frequency other than a low or audible frequency, as herein defined, my invention may be practiced in that case also by a suitable choice of the impedance characteristics of the transformer AT1.

It will also be noted that while I have shown, in my preferred embodiment, the grounded filament lead to tubes VT1 and VT; connected to a nodal point of the coil L1, it is obvious to those skilled in the art that the benefits of my inven tion may still be realized if the connection be removed from the nodal point, the benefits however being inversely proportionate to the degree of removal. 7

Having described my invention I claim:

1. The method of amplifying high frequency electrical currents modulated at audible frequencies which consists of converting the high frequency currents into a plurality of high frequency currents out of phase with each other, amplifying thesehigh frequency currents in two parallel vacuum tube circuits, combining the amplified currents, reducing the combined currents to audible frequency currents corresponding to the modulations of the high frequency currents, transferring the audible frequency currents to the radio frequency circuits and amplifying said audible frequency currents through the high frequency amplifying circuits.

2. The method of reducing high frequency electrical currents modulated at low frequencies to amplified low frequency currents characteristic of said modulations which consists of converting the said high frequency currents into opposite currents differing 180 degrees phase with each other, employing, the alternating high frequency potentials of said converted currents to produce amplified high frequency currents, combining the amplified currents, reducing the resultant amplified currents to low frequency currents corresponding to the modulations thereof, and amplifying said low frequency currents corresponding to the modulations thereof, and amplifying said low frequency currents simultaneously with the amplification of subsequent high frequency currents.

3. In a system for receiving and amplifying electrical currents a pair of three electrode vacuum tubes, means for receiving high frequency electrical currents, means for converting the said high frequency currents into opposite currents differing in phase with each other, means for applying the varying potentials of said opposite currents to the grids of said tubes, means for combining the resultant plate currents of said tubes, means for rectifying said combined currents to produce low frequency currents, and

means for returning said low frequency currents to said vacuum tubes for further amplification in low frequency form.

4. In a system for receiving and amplifying electrical currents a pair of three electrode vacuum tubes, means for receiving high frequency electrical currents, means for converting the said high frequency currents into opposite currents differing degrees in phase with each other, means for applying the varying potentials of said opposite currents to the grids of said tubes, means for combining-the resultant plate currents of said tubes, means for rectifying said combined currents to produce low frequency currents and means for returning said low frequency currents to said vacuum tubes for further amplification in low frequency form.

5. In a receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and sources of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a tuning condenser in parallel with the input coil, a connection between the central tap of the input coil and the filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tube connected together through an inductance, a tuning condenser in parallel with the inductance, a tap centrally located with respect to the terminals of the inductance, a connection from the tap through an indicating device and a source of plate power to the filaments of the vacuum tubes, an inductance coupled to the inductance in the plate ircuits of the first and second vacuum tubes, a tuning condenser for this inductance, one terminal of this inductance coupled to the grid of a third vacuum tube functioning as a. detector, the other terminal of this inductance connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer and the source of plate power to the filaments of the vacuum tube.

6. In a receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and sources of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a plurality of tuning condensers in parallel with the input coil, a connection between the central tap of the input coil and the filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tube connected together through a plurality of inductances, a plurality of tuning condensers in parallel with the inductances, a tap between the inductances, a connection from the tap through an indicating device and a source of plate current to the filaments of the vacuum tubes, a plurality of inductances coupled to the inductances in the plate circuits of the first and second vacuum tubes, a tuning condenser for these inductances, one terminal of these inductances coupled to the grid of a third vacuum tube functioning as a detector, the other terminal of these inductances connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer and the source of plate power to the filaments of the vacuum tubes.

7. In a receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and sources of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a plurality of tuning condensers in parallel with the input coil, the central element of the tuning condensers being grounded, a connection between the central tap of the input coil and the grounded filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tubes being connected together through an inductance, a tuning condenser in parallel with the inductance, a tap centrally located with respect to the terminals of the inductance, a connection from the tap through an indicating device and a source of plate current to the filaments of the vacuum tubes, an inductance coupled to the inductance in the plate circuits of the first and second vacuum tubes, a tuning condenser for this inductance, one terminal of this inductance coupled to the grid of a third vacuum tube functioning as a detector, the other terminal of this inductance connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer and the source of plate power to the filaments of the vacuum tubes. l l

8. In a receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and source of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a tuning condenser in parallel with the input coil, a connection between the central tap of the input coil and the filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tubes being connected together through an inductance, two resistances and a second inductance, a plurality of tuning condensers in parallel with the inductances and resistances, a tap between the resistances, a connection from the tap through an indicating device and a source of plate current to the filaments of the vacuum tubes, a plurality of inductances coupled to the inductances in the plate circuits of the first and second vacuui'n tubes; a tuning condenser for these inductances, one terminal of these inductances coupled to the grid of a third vacuum tube functioning as a detector, the other terminal of these inductances connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer and the source of plate power to the filaments of the vacuum tubes.

9. In a reflex system including high frequency and low frequency circuits, means for eliminating the flow of high frequency current between the points in the high frequency circuit at which the low frequency potential is returned to thehigh frequency circuit.

10. In a reflex circuit including a reflex coupling, means for eliminating the flow of high frequency currents between the points at which said coupling is connected to the high frequency circuit.

ll. In a system for receiving and amplifying electrical currents a circuit responsive to a high frequency, a circuit responsive to a lower frequency, a reflex coupling between said circuits, and means for eliminating the flow of high. frequency currents between the points in said circuit responsive to a high frequency at which the circuit responsive to a lower frequency is connected.

12. In a receiving and amplifying system, a high frequency circuit, a rectifier circuit therefor, a reflex. coupling between said rectifier circult and said high frequency circuit, and means for eliminating the flow of high frequency between the points in said high frequency circuit at which the reflex coupling is connected to the high frequency circuit.

13. In a system for receiving and amplifying electrical currents having an envelope with definite frequency characteristics, a circuit for receiving said electrical currents, means foramplifying said currents, means for deriving from said electrical currents a voltage proportionate to said frequency characteristics, and means for impressing said voltage upon said circuit between substantially nodal points in said circuit.

14. In a system for receiving and amplifying electrical currents including a high frequency circuit, a rectifier circuit therefor, a reflex coupling between said circuits and means for preventing high frequency current flow between the points in said high frequency circuit to which said coupling is reflexed and thereby preventing said currents from entering the rectifier circuit through said coupling.

15. In a receiving and amplifying system, a plurality of circuits in cascade relation, means for applying the potentials of one of said circuitsto a'preceding circuit between substantially nodal points in said preceding circuit.

16. In a receiving and amplifying system of the reflex type, a plurality of thermionic tubes connected in push-pull relation for amplifying the received currents, and means for applying refiexed currents to said tubes in parallel relation for amplifying the reflexed currents.

17. In a receiving and amplifying system of the reflex type, a plurality of thermionic tubes connected in push-pull relation for amplifying the received currents, and means for applying the reflexed currents to said tubes between substantially nodal points said means connecting said tubes to function in parallel relation for amplifying said refleXed currents.

18. In a system for receiving and amplifying electrical currents having an envelope with definite frequency characteristics, a plurality of thermionic tubes, means connected in push-pull relation for amplifying the received currents, means for deriving from the amplified currents a voltage proportionate to said frequency characteristics, and connections whereby said tubes will operate in parallel relation for amplifying said derived voltage.

19. In a receiving and amplifying system of the reflex type, a plurality of thermionic tubes connected in push-pull relation for amplifying received radio frequency currents, means connect.- ed in the output ofsaid amplifier for detecting said radio frequency currents, and means for applying the detected component tosaid thermionic tubes in parallel relation.

20. In a receiving and amplifying system of the reflex type, a plurality of thermionic tubes connected in push-pull relation for amplifying the received currents, means for detecting the amplified currents, means for applying the detected currents to the tubes between substantially nodal points, and means for connecting said tubes to function in parallel relation for amplifying the detected currents.

JAB/[ES E. PARKER. 

